Extraordinary/Enhanced optical transmission (EOT) is studied in the realization of plasmonic based filters in the visible range and near infrared spectrum for the purpose of substituting the Bayer-pattern filter with a new CMOS-compatible filter which can be easily tuned to provide different filter spectra. The filters studied in this paper are based on nano-structured 150nm thick Aluminum (Al) layer sandwiched between silicon dioxide (SiO<sub>2</sub>) layers. The resonance wavelengths achieved by the filters are at 700nm and 950 nm. Three parameters are used for tuning the two filters, i.e., aperture area, the period, and the holes arrangement (square or rhombic lattice). The filter is based on the principle of surface plasmon polaritons (SPPs), where the electromagnetic waves of the incident light couples with the free charges of the metal at the metal-dielectric interface. EOT is observed when the metal is structured with apertures such as rectangular, circular, cross, bowtie, etc. The resonance frequency in that case depends on the shape of the aperture, material used, the size of the apertures, the period of the array, and the surrounding material. The fabricated two filters show EOT at wavelengths as designed and simulated with blueshift in the peak location.
HDRC (high dynamic range CMOS) allows for more than 120 dB signal range in image processing. Scene details with
both very high and extremely low radiant flux may thus appear within the same image. Color constancy over the entire
signal range and good high speed performance are further aspects of this logarithmic imager technology. These features
qualify HDRC cameras for thermography, since the signal range of Planck's temperature radiation in a two dimensional
array is comparable to HDRC's intensity range. Especially in material welding and laser cutting processes, in high power
light sources and in high temperature material processing, fast monitoring of the spacial and dynamic temperature
distributions present a challenge to conventional thermal imaging and thus call for innovative concepts. A particular
challenge is in the compensation of the emissivity of the radiating surface.
Here, we present a new concept based on a modified HDRC VGA color camera, allowing for visualization and
measurement of temperatures from about 800 °C up to 2300 °C. The modifications include an optical filter for
minimizing UV and IR straylight and a notch filter for clipping off the green optical range in order to separate the blue
and red RGB regions. An enhanced and adapted software provides a division of the neighboured red and blue pixel
signals by means of simply subtracting the HDRC signals. As a result the local temperature information of the
visualized scene spot is independent of emissivity.
This is, to our knowledge, the first demonstration of a high speed thermal imager to date.